The present invention relates to a hybrid vehicle using a generator, a motor and an electric energy storage means to realize a low fuel consumption drive by an engine.
As a drive system which can attain a low fuel consumption of an engine for driving a vehicle, there is known a hybrid type which utilizes a driving force of a motor. The hybrid type is classified into a series hybrid type wherein a vehicle is driven by a motor using a generated output of a generator driven by an engine and a parallel hybrid type wherein a driving force generated by an engine and a driving force generated by a motor are combined together mechanically to drive a vehicle. Also known is a series-parallel type as a combination of both such series hybrid type and parallel hybrid type.
For example, in Japanese Patent Laid-open No. Hei 8-98322 there is disclosed a series-parallel hybrid type wherein, in a low-speed vehicular running, the clutch is released, or turned off, whereby the driving mode becomes a series hybrid mode. In the series hybrid mode, an engine can be operated in a high efficiency to generate electric power by increasing the engine speed. While the vehicle is running at a high speed, a parallel hybrid mode is selected by engaging the clutch, or turning on the clutch, thereby permitting a highly efficient operation by the engine. Further, in this conventional type, for preventing a frequent, intermittent on-off operation of the clutch, there is adopted a method wherein a mode switching vehicle speed is given hysteresis.